PayPlans is an open-source membership software for selling your services online. It provides

automatic subscriptions and effortless billing management. The integration with Post Affiliate Pro is possible with an integration plugin.

1.

Get the plugin

The first step is to get the plugin. You can download it from site http://www.readybytes.net/payplans/apps.html#/app/pp-postaffiliatepro

2.

Setup

You can configure the plugin following this documentation:
http://www.jpayplans.com/support/documentation/item/post-affiliate-pro-2.html#gsc.tab=0